III Nitride Crystal Substrate, and Light-Emitting Device and Method of Its Manufacture

ABSTRACT

Toward making available III nitride crystal substrates advantageously employed in light-emitting devices, and light-emitting devices incorporating the substrates and methods of manufacturing the light-emitting devices, a III nitride crystal substrate has a major face whose surface area is not less than 10 cm 2  and, in a major-face principal region excluding the peripheral margin of the major face from its outer periphery to a 5 mm separation from its outer periphery, the total dislocation density is from 1×10 4  cm −2  to 3×10 6  cm −2 , and the ratio of screw-dislocation density to the total dislocation density is 0.5 or greater.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to Group-III nitride crystal substratesadvantageously employed in light-emitting devices, and to light-emittingdevices and methods of their manufacture.

2. Description of the Related Art

Group III nitride crystal substrates find tremendous utility assubstrates for a variety of semiconductor devices includingoptoelectronic device elements and electronic devices. Improving thecharacteristics of the variety of semiconductor devices in which IIInitride crystal substrates are employed mandates that the substrates beof low dislocation density and favorable crystallinity. Furthermore,from a III nitride crystal substrate use-efficiency perspective, asubstrate major-face surface area of 10 cm² or more, preferably 20 cm²or more, is deemed necessary.

Therefore, various techniques for fabricating low-dislocation-densityIII nitride crystal substrates in bulk have been proposed. (Cf., forexample, Japanese Unexamined Pat. App. Pub. No. 2007-161536.)

Therein, Japanese Unexamined Pat. App. Pub. No. 2007-161536 disclosesthat electronic devices including an Al_(x)Ga_(y)In_(1-x-y)N (0≦x, 0≦y,x+y≦1) crystal substrate in which the total dislocation density is from1×10² cm⁻² to 1×10⁶ cm⁻², and an at least single-lamina semiconductorlayer formed onto the substrate have uniform, high breakdown voltages.The document also discloses that from the perspective of heightening thedevice breakdown voltage, screw-dislocation density in the substratesfor the electronic devices is preferably 1×10⁴ cm⁻² or less.

Nevertheless, as to correlations between substrate dislocation densityand the characteristics of semiconductor devices apart from electronicdevices (light-emitting devices for example), Pat. App. Pub. No.2007-161536 stops short of clarity.

BRIEF SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to clarifycorrelations between the dislocation density in III nitride crystalsubstrates and the characteristics of light-emitting devices, therebymaking available III nitride crystal substrates advantageously employedin light-emitting devices, and light-emitting devices incorporating thesubstrates and methods of manufacturing the light-emitting devices.

The present invention in one aspect is a Group-III nitride crystalsubstrate having a major face whose surface area is 10 cm² or more,wherein, in a major-face principal region excluding the peripheralmargin of the major face from its outer periphery to a 5 mm separationfrom its outer periphery, the total dislocation density is from 1×10⁴cm⁻² to 3×10⁶ cm⁻², and the ratio of screw-dislocation density to thetotal dislocation density is 0.5 or greater. In a III nitride crystalsubstrate involving the present invention, the ratio ofscrew-dislocation density to the total dislocation density can be 0.9 orgreater.

The present invention in another aspect is a light-emitting deviceincluding the above-described III nitride crystal substrate, and an atleast single-lamina III nitride layer formed onto the III nitridecrystal substrate.

The present invention in a still a further aspect is a light-emittingdevice manufacturing method including: a step of preparing theabove-described III nitride crystal substrate; and a step of depositingan at least single-lamina III nitride layer onto the III nitride crystalsubstrate.

The present invention affords III nitride crystal substratesadvantageously employed in light-emitting devices, and light-emittingdevices incorporating the substrates and methods of manufacturing thelight-emitting devices.

From the following detailed description in conjunction with theaccompanying drawings, the foregoing and other objects, features,aspects and advantages of the present invention will become readilyapparent to those skilled in the art.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an outline plan view representing a III nitride crystalsubstrate on the major face of which etch pits have formed.

FIG. 2 is an outline sectional view taken along the line II-II in FIG.1, seen in the direction of the arrows.

FIG. 3 is outline sectional views representing one example of aIII-nitride crystal substrate manufacturing method, wherein FIG. 3Arepresents a step of preparing an undersubstrate, FIG. 3B represents astep of growing a III nitride crystal by a liquid-phase technique, andFIG. 3C represents a step of additionally growing a III nitride crystalby a vapor-phase technique.

FIG. 4 is outline sectional views representing another example of aIII-nitride crystal substrate manufacturing method, wherein FIG. 4Arepresents a step of forming a major face on a III nitride crystal grownby a liquid-phase technique, FIG. 4B represents a step of additionallygrowing a III nitride crystal by a liquid-phase technique, and FIG. 4Crepresents a step of additionally growing a III nitride crystal by avapor-phase technique.

FIG. 5 is an outline sectional view of one example of a light-emittingdevice.

FIG. 6 is a graph plotting, for light-emitting devices on III-nitridecrystal substrates, substrate total dislocation density, and therelationship between device emission intensity and the ratio ofscrew-dislocation density to the total dislocation density in the devicesubstrates.

DETAILED DESCRIPTION OF THE INVENTION Embodiment Mode 1

A III nitride crystal substrate involving the present invention has amajor face whose surface area is 10 cm² or greater, with the totaldislocation density being between 1×10⁴ cm⁻² and 3×10⁶ cm⁻² and with theratio of screw-dislocation density to the total dislocation densitybeing 0.5 or greater, in a major-face principal region excluding theperipheral margin of the major face from its outer periphery to a 5 mmseparation from its outer periphery.

A III nitride crystal substrate in the present embodiment mode has amajor face whose surface area is 10 cm² or larger, which enables themanufacture of large-scale light-emitting devices, as well as themass-production of light-emitting devices.

In a III nitride crystal substrate in the present embodiment mode, thetotal dislocation density is between 1×10⁴ cm⁻² and 3×10⁶ cm⁻², with theratio of screw-dislocation density to the total dislocation densitybeing 0.5 or greater, in a principal region of the major face, exceptingthe peripheral margin of the major face from its outer periphery to a 5mm separation therefrom. Referring to FIG. 6, as will be detailed later,light-emitting devices with an at least single-lamina III nitride layerformed onto a III nitride crystal substrate in which the totaldislocation density is between 1×10⁴ cm⁻² and 3×10⁶ cm⁻², and the ratioof screw-dislocation density to the total dislocation density is 0.5 orgreater have higher emission intensities by comparison withlight-emitting devices with an at least single-lamina III nitride layerformed onto a III nitride crystal substrate in which the totaldislocation density is between 1×10⁴ cm⁻² and 3×10⁶ cm⁻², and the ratioof screw-dislocation density to the total dislocation density is lessthan 0.5.

In a III nitride crystal substrate in a further aspect of the presentembodiment mode, the total dislocation density is between 1×10⁴ cm⁻² and3×10⁶ cm⁻², with the ratio of screw-dislocation density to the totaldislocation density being 0.9 or greater, in the principal region of themajor face excepting the peripheral margin of the major face from itsouter periphery to a 5 mm separation therefrom. Referring again to FIG.6, light-emitting devices with an at least single-lamina III nitridelayer formed onto a III nitride crystal substrate in which the totaldislocation density is between 1×10⁴ cm⁻² and 3×10⁶ cm⁻², and the ratioof screw-dislocation density to the total dislocation density is 0.9 ormore have still higher emission intensities by comparison withlight-emitting devices with an at least single-lamina III nitride layerformed onto a III nitride crystal substrate in which the totaldislocation density is between 1×10⁴ cm⁻² and 3×10⁶ cm⁻² and the ratioof screw-dislocation density to the total dislocation density is from0.5 to 0.7.

Herein, the reason evaluation of the total dislocation density and theratio of screw-dislocation density to the total dislocation density arecarried out in the major-face principal region that excludes theperipheral margin of the major face from its outer periphery to a 5 mmseparation from its outer periphery is because it can happen thatdislocations swept out to the outer periphery gather in the peripheralmargin, raising the dislocation density.

The present inventors had previously found that semiconductor devicesformed employing III nitride crystal substrates in which the totaldislocation density is between 1×102 cm⁻² and 1×10⁶ cm⁻² have advancedcharacteristics by comparison with semiconductor devices formed in thesame structure as that of the above semiconductor devices, employing IIInitride crystal substrates in which the total dislocation density isless than 1×10² cm⁻² (cf. Japanese Unexamined Pat. App. Pub. No.2007-161536). The present inventors completed the present invention byfurther discovering that with the total dislocation density beingbetween 1×10⁴ cm⁻² and 3×10⁶ cm⁻², light-emitting devices formedemploying III nitride crystal substrates in which the ratio ofscrew-dislocation density to the total dislocation density is 0.5 orgreater exhibit higher emission intensities by comparison withlight-emitting devices formed employing III nitride crystal substratesin which the ratio of screw-dislocation density to the total dislocationdensity is less than 0.5.

Dislocations that can appear on the major face of a III nitride crystalsubstrate include screw dislocations, edge dislocations, and mixeddislocations in which screw and edge dislocations are intermingled.Furthermore, by etching the major face of a substrate, dislocationsappearing on the substrate major face can be verified as the pitsproduced (“etch pits” hereinafter).

The method of etching the major face of a III nitride crystal substrateis not particularly limited; either liquid-phase etching or vapor-phaseetching may be adopted. In liquid-phase etching, etching solutionspreferably employed include a eutectic mixture of potassium hydrate andsodium hydrate (KOH—NaOH eutectic mixture) at a solution temperature ofsome 300° C. to 500° C., or a solution mixture of phosphoric acid andsulfuric acid (H₃PO₄—H₂SO₄ solution mixture) at a temperature of some200° C. to 300° C. In vapor-phase etching, etching gases containinghalogen gases or halogen compound gases are preferably employed. As ahalogen gas contained in the etching gas, Cl₂ gases or F₂ gases, and asa halogen compound gas, HCl gases, BCl₃ gases or CF₄ gases, may be givenas preferable examples. Herein, from the perspective of enabling theetching a large amount of crystals at once, and of facilitatingpost-etch cleaning operations, vapor-phase etching is more preferable.

Referring to FIGS. 1 and 2, if a major face 100 m of a III nitridecrystal substrate 100 is etched, etch pits 110 p corresponding todislocations 110 appearing on the major face 100 m form. The etch pits110 p are in the form of hexagonal pyramids whose opposing basal edgesare nearly parallel to each other, and for the most part are in the formof regular hexagonal pyramids. Herein, the average distance betweenopposite basal corners of the hexagonal pyramids that are the etch pits110 p is defined as the diameter of an etch pit.

The type of the dislocations 110 can be distinguished by the size of theetch pit 110 p diameter. Etch pits 111 p (referred to as large etch pits111 p hereinafter) having a greater diameter D₁ are based on screwdislocations 111, while etch pits 112 p (referred to as small etch pits112 p hereinafter) having a shorter diameter D₂ are based on edgedislocations 112. Specifically, dislocations are classified into threetypes: screw dislocation, edge dislocation, and mixed dislocation inwhich the screw and edge dislocations are intermingled. It should beunderstood that “screw dislocations” in the present invention refers todislocations that contain screw dislocations, and includes screwdislocations and mixed dislocations.

The absolute value of the diameter of each etch pit varies depending onthe conditions for etching the major face of a substrate, but therelative ratio between the diameters of the large and small etch pits,not being dependent on the etching conditions, is nearly constant.Furthermore, variations occur both in the diameter D₁ of the large etchpits 111 p and in the diameter D₂ of the small etch pits 112 p, and suchthat the ratio D₁:D₂ is approximately 5˜10:1˜2.

In the present application, “dislocations” signifies either theaforementioned screw dislocations (that is, screw dislocations and mixeddislocations are included in the detailed definition) or edgedislocations, and “total dislocations” signifies all the dislocations,including the aforementioned screw dislocations and edge dislocations.Accordingly, “total dislocation density” is density of the totaldislocations per unit area, and is calculated by counting the totalnumber of great and small etch pits per unit area. Furthermore,“screw-dislocation density” is the density of screw dislocations perunit area, and is calculated by counting the number of large etch pitsper unit area.

The method of manufacturing a III nitride crystal substrate in thepresent embodiment mode is not particularly limited; the substrate maybe manufactured by, for example, the following method. First, referringto FIG. 3A, an undersubstrate 10 including a III nitride crystal layer10 a having a major face 10 m, with the major face 10 m having an angleof inclination θ₁ of from 0.50 to 10° with respect to a {0001} plane 10c of the III nitride crystal layer 10 a is prepared (step of preparingan undersubstrate).

Next, referring to FIG. 3B, a III nitride crystal 20 is grown onto themajor face 10 m of the undersubstrate 10 by a liquid-phase technique(step of growing a III nitride crystal). Herein, the liquid-phasetechnique is not particularly limited, but from the perspective ofepitaxially growing low-dislocation-density crystals efficiently, amethod in which the undersubstrate is arranged so that its major facecontacts with a melt containing a Group III elemental metal, and anitrogen-containing gas (such as gaseous nitrogen) is supplied to themelt, to grow a III nitride crystal onto the major face of theundersubstrate is preferable. The melt is not particularly limited aslong as it contains a III-elemental metal; a molten Group-III metal(solution or self-flux technique), or a melt (flux technique) of aIII-elemental metal and a metal (such as Na, Li and other alkali metals,Ca and other alkali earth metals, and Cu, Ti, Fe, Mn, Cr and othertransition metals) serving as a solvent for the III elemental-metal isutilized, for example.

On the major face 10 m of the undersubstrate 10, a plurality of(not-illustrated) micro-steps consisting of a plurality of(not-illustrated) terraced faces paralleling a {0001} plane 10 c, and ofa plurality of (not-illustrated) stepped planes having a given anglewith respect to the {0001 } plane are formed.

Growing the III nitride crystal 20 onto the major face 10 m by aliquid-phase technique leads to crystal growth in the direction parallelto, and in the direction perpendicular to, the terraced faces.Furthermore, the crystal-growth rate in the direction parallel to theterraced faces is more rapid by comparison with the crystal-growth ratein the direction perpendicular to the terraced faces. Herein, edgedislocations propagate parallel to the crystal growth direction. Theedge dislocations therefore propagate substantially paralleling theterraced faces. That is, the dislocation propagation angle φ_(E) formedby the edge-dislocation propagation line 20 de and the {0001} planes 10c and 20 c is small, being some 0° to 5°. In contrast, screwdislocations propagate in a direction having an angle of inclination of30° to 45° with respect to the crystal growth direction. That is, thedislocation propagation angle φ_(S) formed by the screw-dislocationpropagation line 20 ds and the {0001 } planes 10 c and 20 c is large,being some 45° to 60°.

Accordingly, employing the above undersubstrate 10 results in thatcompared with screw dislocations, edge dislocations are more efficientlyswept out to the outer periphery of crystal, reducing total dislocationdensity, and heightening ratio of screw-dislocation density to the totaldislocation density.

Herein, how dislocations in crystal are transmitted (dislocationtransmitting lines 20 de and 20 ds) can be observed by light-scatteringtomography. Furthermore, the {hklm} planes and <hklm> directions incrystal can be identified by X-ray diffraction. It will be appreciatedthat the {hklm} planes (herein h, k, l and m are Miller indexes, dittohereinafter) are a generic term for the planes including the (hklm)plane and planes crystallographically equivalent to the (hklm) plane.Likewise, the <hklm> directions are a generic term for the directionsincluding the [hklm] direction and the directions crystallographicallyequivalent to the [hklm] direction.

Here, from the perspective of crystal symmetry, the tilt vector 10 h ofthe major face 10 m of the undersubstrate 10 is preferably inclined in a<1-100> direction or in a <11-20> direction with respect to a <0001>direction.

Furthermore, referring to FIG. 3B, the surface 20 s of the III nitridecrystal 20 grown by a liquid-phase technique in the above manner isplanarized by grinding or polishing to form a major face 20 nparalleling the {0001} planes 10 c and 20 c.

Next, referring to FIG. 3C, a III nitride crystal 40 may be additionallygrown onto the major face 20 n of the III nitride crystal 20 by avapor-phase technique. The vapor-phase technique is not particularlylimited, but from the perspective of epitaxially growinglow-dislocation-density crystals efficiently, preferable techniquesinclude hydride vapor phase epitaxy (HVPE), metalorganic chemical vapordeposition (MOCVD), and molecular beam epitaxy (MBE). Among thesetechniques, from the perspective of rapid crystal-growth rate inparticular, HVPE is preferable. That is, additionally growing by HVPEthe III nitride crystal 40 onto the major face 20 n of the III nitridecrystal 20 enables reducing total dislocation density andscrew-dislocation density in the III nitride crystal 40 as it grows.Herein, in the growth of the III nitride crystal 40, the ratio betweenedge-dislocation density and screw-dislocation density only slightlyvaries because the extent of the dislocation reduction with the growthis small. In other words, ratio of screw-dislocation density to totaldislocation density also only slightly varies.

Herein, as illustrated in FIG. 3C, the III nitride crystal 40 is slicedin a plurality of planes 40 q and 40 r paralleling the {0001} planes 10c and 20 c, and the cut surfaces are planarized by grinding orpolishing, to produce a large number of III nitride crystal substrates40 p in which dislocation density has been reduced.

Furthermore, referring to FIG. 4A, the surface of the III nitridecrystal 20 grown by a liquid-phase technique is ground or polished toform a major face 20 m having an angle of inclination θ₂ of from 0.5° to10° with respect to the {0001 } planes 10 c and 20 c.

Next, referring to FIG. 4B, a III nitride crystal 30 may be additionallygrown onto the major face 20 m of the III nitride crystal 20 by aliquid-phase technique. The liquid-phase technique is not particularlylimited, but from the perspective of growing epitaxiallylow-dislocation-density crystal efficiently, a method in which anundersubstrate is arranged so that its major face contacts with a meltcontaining a III-elemental metal, and a nitrogen-containing gas (such asa nitrogen gas) is supplied to the melt, to grow a III nitride crystalonto the major face of the undersubstrate—for example, solution or fluxtechnique—is preferable. Herein, on the major face 20 m of the IIInitride crystal 20, owing to the angle of inclination θ₂ with respect tothe {0001} planes 10 c and 20 c, as on the major face 10 m of theundersubstrate 10, a plurality of (not-illustrated) micro-stepsconsisting of a plurality of (not-illustrated) terraced facesparalleling the {0001 } planes 10 c and 20 c, and of a plurality of(not-illustrated) stepped planes having a given angle with respect to a{0001} plane form.

Growing the III nitride crystal 30 onto the major face 20 m by aliquid-phase technique leads to crystal growth in the direction parallelto, and in the direction perpendicular to, the terraced faces.Furthermore, crystal-growth rate in the direction parallel to theterraced faces is more rapid by comparison with crystal-growth rate inthe direction perpendicular to the terraced faces. Herein, edgedislocations propagate parallel to the crystal growth direction. Theedge dislocations therefore propagate substantially paralleling theterraced faces. That is, the dislocation propagation angle φ_(E) formedby the edge-dislocation propagation line 20 de and the {0001} planes 10c and 20 c is small, being some 0° to 5°. In contrast, screwdislocations propagate in a direction having an angle of inclination of30° to 45° with respect to the crystal growth direction. That is, thedislocation propagation angle φ_(S) formed by the screw-dislocationpropagation line 20 ds and the {0001 } planes 10 c and 20 c is large,being some 45° to 60°.

Accordingly, additionally growing the III nitride crystal 30 onto themajor face 20 m of the III nitride crystal 20 by liquid-phase techniqueresults in that edge dislocations are more efficiently swept out to theouter periphery of crystal by comparison with screw dislocations.Therefore, in the III nitride crystal 30 by comparison with in the IIInitride crystal 20, total dislocation density is further reduced, andthe ratio of screw-dislocation density to the total dislocation densityis made greater.

Here, from the perspective of crystal symmetry, the tilt vector 20 h ofthe major face 20 m of the III nitride crystal 20 is preferably inclinedin a <1-100> direction or in a <11-20> direction with respect to a<0001> direction. Moreover, from the perspective of further reducing thetotal dislocation density, and of making the ratio of screw-dislocationdensity to the total dislocation density greater, the tilt vector 20 hof the major face 20 m of the III nitride crystal 20 more preferablydiffers in orientation from the tilt vector 10 h of the major face 10 mof the undersubstrate 10.

As just described, repeating the formation, onto a grown III nitridecrystal, of a major face having an angle of inclination of 0.5° to 10°with respect to a {0001 } plane, and the growth of a III nitride crystalonto the major face by a liquid-phase technique enables reducing furthertotal dislocation density, and making the ratio of screw-dislocationdensity to the total dislocation density greater.

Moreover, referring to FIG. 4B, the surface 30 s of the III nitridecrystal 30 grown by a liquid-phase technique in the above manner isplanarized by grinding or polishing to form a major face 30 nparalleling the {0001} planes 10 c and 20 c.

Next, referring to FIG. 4C, a III nitride crystal 50 may be additionallygrown onto the principal surface 30 n of the III nitride crystal 30 by avapor-phase technique. The vapor-phase technique is not particularlylimited, but from the perspective of epitaxially growinglow-dislocation-density crystals efficiently, preferable techniquesinclude HVPE, MOCVD, and MBE. Among these techniques, from theperspective of rapid crystal-growth rate, HVPE is particularlypreferable. That is, additionally growing by HVPE the III nitridecrystal 50 onto the major face 30 n of the III nitride crystal 30 makesit possible to reduce the total dislocation density andscrew-dislocation density in the III nitride crystal 50 as it grows.Herein, in the growth of the III nitride crystal 50, the ratio betweenedge-dislocation density and screw-dislocation density only slightlyvaries because the extent of the dislocation reduction with the growthis small. In other words, the ratio of screw-dislocation density to thetotal dislocation density also only slightly varies.

Herein, as illustrated in FIG. 4C, the III nitride crystal 50 is slicedin a plurality of planes 50 q and 50 r parallel to {0001} planes 10 c,20 c and 30 c, and the cut surfaces are planarized by grinding orpolishing, to produce a large number of III nitride crystal substrates50 p in which the dislocation density has been lowered.

Accordingly, appropriately combining the above crystal growth methodslowers total dislocation density, and heightens ratio ofscrew-dislocation density to the total dislocation density by comparisonwith an undersubstrate or a III nitride crystal serving as theundersubstrate, leading to III nitride crystals and III nitride crystalsubstrates in which the total dislocation density is between 1×10⁴ cm⁻²and 3×10⁶ cm⁻², with the ratio of screw-dislocation density to the totaldislocation density being 0.5 or greater.

Embodiment Mode 2

Referring to FIG. 5, a light-emitting device involving the presentinvention includes a III nitride crystal substrate 100 in EmbodimentMode 1, and an at least single-lamina III nitride layer 130 formed ontothe III nitride crystal substrate 100. A light-emitting device in thepresent embodiment mode includes an at least single-lamina III nitridelayer formed onto a III nitride crystal substrate in which the totaldislocation density is between 1×10⁴ cm⁻² and 3×10⁶ cm⁻², with the ratioof screw-dislocation density to the total dislocation density being 0.5or greater. Therefore, the device has high emission intensity, as shownin FIG. 6.

Specifically, referring to FIG. 5, in the light-emitting device in thepresent embodiment mode, as an at least single-lamina III nitride layer130, onto a first major face of a GaN substrate (III nitride crystalsubstrate 100) of 1 mm×1 mm×500 μm in thickness, in which the totaldislocation density is between 1×10⁴ cm⁻² and 3×10⁶ cm⁻², with the ratioof screw-dislocation density to the total dislocation density being 0.5or greater, the following layers are successively deposited: a 2μm-thick n-type GaN layer 131 doped with Si; a 100 nm-thick emissionlayer 132 having a multiquantum well structure constituted by six pairsof an In_(0.01)Ga_(0.99)N barrier layer and an In_(0.1)Ga_(0.9)N welllayer; a 20 nm-thick p-type Al_(0.18)Ga_(0.82)N layer 133 doped with Mg;and a 50 nm-thick p-type GaN layer 134 doped with Mg. Furthermore, aNi/Au electrode of 0.2 mm×0.2 mm×0.5 μm in thickness, serving as ap-side electrode 141 is formed onto a part of the p-type GaN layer 134.Moreover, a 1 μm-thick Ti/Al electrode serving as an n-side electrode142 is formed onto a second major face of the GaN substrate (III nitridecrystal substrate 100).

Embodiment Mode 3

Referring to FIG. 5, one embodiment mode of a light-emitting devicemanufacturing method involving the present invention includes a step ofpreparing a III nitride crystal substrate 100 in Embodiment Mode 1, anda step of forming an at least single-lamina III nitride layer 130 ontothe III nitride crystal substrate 100. According to the light-emittingdevice manufacturing method in the present embodiment mode, forming theat least single-lamina III nitride layer 130 onto the III nitridecrystal substrate 100 in which the total dislocation density is between1×10⁴ cm⁻² and 3×10⁶ cm⁻², with the ratio of screw-dislocation densityto the total dislocation density being 0.5 or greater makes it possibleto manufacture light-emitting devices having high emission intensity.

The light-emitting device manufacturing method in the present embodimentmode is provided with the step of preparing the III nitride crystalsubstrate 100 in Embodiment Mode 1. The step of preparing a III nitridecrystal substrate in which the total dislocation density is between1×10⁴ cm⁻² and 3×10⁶ cm⁻², with the ratio of screw-dislocation densityto the total dislocation density being 0.5 or greater is notparticularly limited, but from the perspective of efficientlymanufacturing the substrates, the preparation is preferably carried outby the method described in Embodiment Mode 1.

The light-emitting device manufacturing method in the present embodimentmode is additionally provided with the step of forming the at leastsingle-lamina III nitride layer 130 onto the III nitride crystalsubstrate 100. The method of forming a III nitride layer is notparticularly limited, but from the perspective of growinglow-dislocation-density epitaxial layers, techniques preferably employedinclude HVPE, MOCVD, and MBE. From the perspective of being high inproductivity and reliability, MOCVD is more preferably employed.

In the step of forming the at least single-lamina III nitride layer 130onto the III nitride crystal substrate 100, onto a first major face of aGaN substrate of 50.8 mm (2 inches) in diameter×500 μm in thickness,serving as a III nitride crystal substrate 100, the following layers aresuccessively grown by, for example, MOCVD: a 2 μm-thick n-type GaN layer131 doped with Si; a 100 nm-thick emission layer 132 having amultiquantum well structure constituted by six pairs of anIn_(0.01)Ga_(0.99)N barrier layer and an In_(0.1)Ga_(0.9)N well layer; a20 nm-thick p-type Al_(0.18)Ga_(0.82)N layer 133 doped with Mg; and a 50nm-thick p-type GaN layer 134 doped with Mg.

Furthermore, onto a part of the p-type GaN layer 134, a 0.5 μm-thickNi/Au electrode serving as a p-side electrode 141 is formed by (vacuum)evaporation. Likewise, onto a second major face of the GaN substrate(III nitride crystal substrate 100), a 1 μm-thick Ti/Al electrodeserving as an n-side electrode 142 is formed by evaporation.

Next, wafers in which the at least single-lamina III nitride layer 130is formed onto the III nitride crystal substrate 100 are divided intochips of the predetermined size to manufacture light-emitting devices ofthe predetermined size.

Embodiments Embodiment 1 1. III-Nitride Crystal Substrate Preparation

A GaN undersubstrate of 50.8 mm (2 inches) in diameter×500 μm inthickness, having a major face having an angle of inclination of 5° withrespect to the (0001) plane, with the total dislocation density being1×10⁷ cm⁻², and with the ratio of screw-dislocation density to the totaldislocation density being 0.1 was employed to grow, by combining thesolution technique (liquid-phase technique) described in Embodiment Mode1 with HVPE (vapor-phase technique), a plurality of GaN crystals having,with total dislocation densities ranging from 5×10 cm⁻² to 5×10⁶ cm⁻²,ratios of screw-dislocation density to total dislocation density; andGaN substrates that were each 50.8 mm (2 inches) in diameter×500 μm inthickness were fabricated from these GaN crystals. Herein, as to the GaNcrystal growth conditions in the flux method, the temperature of moltenGa was brought to 1000° C., and the N₂ gas pressure was brought to 10MPa. Furthermore, in conditions for growing the GaN crystals by HVPE,partial pressure of a Ga chloride gas was brought to 10 kPa, partialpressure of a NH₃ gas was brought to 100 kPa, and the crystal growthtemperature was made 1100° C.

The plurality of fabricated GaN substrates were classified into threegroups: a group (“Group R” hereinafter) consisting of a plurality of GaNsubstrates in which the ratio of screw-dislocation density to the totaldislocation density was less than 0.5; a group (“Group A” hereinafter)consisting of a plurality of GaN substrates in which the ratio ofscrew-dislocation density to the total dislocation density was between0.5 and 0.7 ; and a group (“Group B” hereinafter) consisting of aplurality of GaN substrates in which the ratio of screw-dislocationdensity to the total dislocation density was 0.9 or more.

2. Light-Emitting Device Formation

Next, as an at least single-lamina III nitride layer 130, onto a firstmajor face of the plurality of GaN substrates (III nitride crystalsubstrates 100) of 50.8 mm (2 inches) in diameter×500 μm in thickness ineach of the groups, the following layers were successively grown byMOCVD: a 2 μm-thick n-type GaN layer 131 (carrier concentration: 2×10¹⁸cm⁻³) doped with Si; a 100 nm-thick emission layer 132 having amultiquantum well structure constituted of six pairs of anIn_(0.01)Ga_(0.99)N barrier layer and an In_(0.1)Ga_(0.9)N well layer; a20 nm-thick p-type Al_(0.18)Ga_(0.82)N layer 133 (carrier concentration:3×10¹⁷ cm⁻³) doped with Mg; and a 50 nm-thick p-type GaN layer 134(carrier concentration: 1×10¹⁸ cm⁻³) doped with Mg.

Subsequently, as a p-side electrode 141, a Ni/Au electrode of 0.2mm×0.2mm×0.5 μm in thickness was formed by vacuum evaporation techniquein the two directions orthogonal to each other on the p-type GaN layer134 at a pitch of 1 mm. Likewise, onto a second major face of the GaNsubstrates (III nitride crystal substrates 100), as an n-side electrode142, a 1 μm-thick Ti/Al electrode was formed by (vacuum) evaporation.

Next, wafers in which an at least single-lamina III nitride layer 130was formed onto a GaN substrates were divided into a plurality of chipsof 1 mm×1 mm—that is, into light-emitting devices—so that each p-sideelectrode came to the central part of each of the chips. Thelight-emitting devices manufactured in this manner were blue-violetlight-emitting diodes (LEDs) having emission peak wavelength of 405 nm.

For corresponding light-emitting devices for each group, fabricatedemploying GaN substrates of each group, emission intensities integratedover an emission wavelength range of from 385 nm to 425 nm weremeasured. The measurements of total dislocation density and emissionintensity for the plurality of light-emitting devices are entered in thetable, while the relationship between the total dislocation density andemission intensity for the plurality of light-emitting devices isgraphed in FIG. 6. Herein, “—” in the table indicates “unmeasured.”Furthermore, in FIG. 6: the line R represents the relationship betweentotal dislocation density and emission intensity for light-emittingdevices in which an at least single-lamina nitride semiconductor layerwas formed onto a Group-R III nitride crystal substrate (termed Group Rlight-emitting devices); the line A represents the relationship betweentotal dislocation density and emission intensity in light-emittingdevices in which an at least single-lamina nitride semiconductor layerwas formed onto a Group-A III nitride crystal substrate (termed Group Alight-emitting devices); and the line B represents the relationshipbetween total dislocation density and emission intensity inlight-emitting devices in which an at least single-lamina nitridesemiconductor layer was formed onto a Group-B III nitride crystalsubstrate (termed Group B light-emitting devices).

TABLE Group R Group A Group B Integrated Integrated Emission Totalemission Total emission Total intensity dislocation intensitydislocation intensity dislocation integral density (arbitrary density(arbitrary density (arbitrary (cm⁻³) units) (cm⁻³) units) (cm⁻³) units)5.0 × 10¹ 0.85 4.0 × 10¹ 0.86 6.5 × 10¹ 0.87 1.0 × 10² 0.91 1.0 × 10²0.896 3.7 × 10² 0.95 2.4 × 10² 0.97 6.0 × 10² 0.99 6.5 × 10² 0.98 1.0 ×10³ 1.00 1.2 × 10³ 1.02 2.1 × 10³ 1.00 3.0 × 10³ 1.02 4.0 × 10³ 1.00 2.9× 10³ 1.02 7.0 × 10³ 0.99 9.0 × 10³ 1.01 6.2 × 10³ 0.99 1.2 × 10⁴ 1.011.5 × 10⁴ 1.03 9.8 × 10³ 1.03 2.7 × 10⁴ 1.00 4.2 × 10⁴ 1.01 2.7 × 10⁴0.99 5.8 × 10⁴ 1.01 7.0 × 10⁴ 0.99 4.8 × 10⁴ 1.02 7.6 × 10⁴ 0.99 1.1 ×10⁵ 1.00 6.6 × 10⁴ 1.02 1.0 × 10⁵ 0.98 3.8 × 10⁵ 1.01 2.0 × 10⁵ 1.03 4.0× 10⁵ 0.96 5.0 × 10⁵ 0.99 3.7 × 10⁵ 1.01 7.0 × 10⁵ 0.94 1.1 × 10⁶ 0.967.1 × 10⁵ 1.02 1.0 × 10⁶ 0.92 3.1 × 10⁶ 0.92 2.5 × 10⁶ 0.97 3.0 × 10⁶0.89 4.5 × 10⁶ 0.88 3.0 × 10⁶ 0.98 5.0 × 10⁶ 0.86 — — 6.1 × 10⁶ 0.88

As is apparent from the table and FIG. 6, with total dislocation densitybeing in the range from 1×10⁴ cm⁻² to 3×10⁶ cm⁻², light-emitting devices(devices in the Group A) with a plurality of III nitride layersdeposited onto a III nitride crystal substrate in which the ratio ofscrew-dislocation density to the total dislocation density is 0.5 orgreater have higher emission intensities by comparison withlight-emitting devices (devices in Group R) with a plurality of IIInitride layers deposited onto a III nitride crystal substrate in whichratio of screw-dislocation density to the total dislocation density isless than 0.5.

Furthermore, with total dislocation density being in the range from1×10⁴ cm⁻² to 3×10⁶ cm⁻², light-emitting devices (devices in Group B)with a plurality of III nitride layers deposited onto a III nitridecrystal substrate in which ratio of screw-dislocation density to thetotal dislocation density is 0.9 or more have still higher emissionintensities by comparison with the light-emitting devices (devices inGroup A) with a plurality of III nitride layers deposited onto a IIInitride crystal substrate in which ratio of screw-dislocation density tothe total dislocation density is 0.5 or greater.

The presently disclosed embodiment modes and embodiments should in allrespects be considered to be illustrative and not limiting. The scope ofthe present invention is set forth not by the foregoing description butby the scope of the patent claims, and is intended to include meaningsequivalent to the scope of the patent claims and all modificationswithin the scope.

1. A Group-III nitride crystal substrate having a major face whosesurface area is not less than 10 cm², wherein, in a major-face principalregion excluding the peripheral margin of the major face from its outerperiphery to a 5 mm separation from its outer periphery, the totaldislocation density is between 1×10⁴ cm⁻² and 3×10⁶ cm⁻² inclusive, andthe ratio of screw-dislocation density to the total dislocation densityis 0.5 or greater.
 2. A III-nitride crystal substrate as set forth inclaim 1, wherein the ratio of the screw-dislocation density to the totaldislocation density is 0.9 or greater.
 3. A light-emitting devicecomprising: a III-nitride crystal substrate as set forth in claim 1; andan at least single-lamina III nitride layer formed onto the III nitridecrystal substrate.
 4. A light-emitting device comprising: a III-nitridecrystal substrate as set forth in claim 2; and an at least single-laminaIII nitride layer formed onto the III nitride crystal substrate.
 5. Alight-emitting device manufacturing method, comprising: a step ofpreparing a III nitride crystal substrate as set forth in claim 1; and astep of forming an at least single-lamina III nitride layer onto the IIInitride crystal substrate.
 6. A light-emitting device manufacturingmethod, comprising: a step of preparing a III nitride crystal substrateas set forth in claim 2; and a step of forming an at least single-laminaIII nitride layer onto the III nitride crystal substrate.